Garrett, the league's No. 1 pick, left Browns practice early on Wednesday with a right ankle injury and did not return. It was the first full day of preparation for the Steelers, who will play in the opener here on Sunday.

"He went as long as he could," said coach Hue Jackson, who seemed concerned it could be serious and acknowledged that Garrett's status for the opener is in doubt.

"We'll see where we are as we move through the week," he said. "Obviously he didn't finish practice.''

Garrett will undergo further evaluation on the ankle, which will likely include an MRI.

Jackson said he didn't think it was the same ankle that Garrett injured on June 14th during minicamp. In that instance, when Cam Erving stepped on his left ankle, he suffered a lateral foot sprain that sidelined him for several weeks.

When he left the Browns facility in June to head home for the summer break, he was spotted in a left walking boot at Cleveland Hopkins International Airport. He returned for training camp on July 27 ready to go, but was somewhat limited at the outset.

He suffered a high left ankle sprain that hampered him all last season at Texas A&M. As a result, he finished with only 8.5 sacks, down from 11.5 in 2015 and 11.0 in 2014.

The injury came just hours after Garrett addressed the media and stood by his draft day remarks that he's coming to 'chop down' Roethlisberger. He stressed that 'you can't be afraid to take somebody down.'

Former Browns cornerback Joe Haden, who signed with the Steelers last week, knows how much of a blow it will be if the Browns have to play without Garrett.

"He's looking like the first overall pick,'' Haden said on a conference call Wednesday. "I was super excited when we got him. I feel like that's the pick that is a stamp. We didn't miss on that one. I could tell that from the very beginning. He just has stuff that you can't teach - his motor, his professionalism and his attitude.

"He definitely is a pro already. He is mature beyond his age. He just loves the game and loves getting after it. My bold prediction, I really feel like Myles can make the Pro Bowl his rookie year."

Given Garrett's injury and his importance to the team, the Browns will be extra cautious. In June they got a solicited a second opinion from foot specialist Dr. Robert Anderson of OrthoCarolina.

Garrett will undergo a series of exams on the ankle, and a source close to the team said the Browns are worried the injury could sideline him for weeks. That would cast a huge pall on the beginning of the season, which includes three AFC North games in the first four weeks.

They've been extremely optimistic about their much-improved defense, in large part because of Garrett and fellow first-round pick Jabrill Peppers.

If Garrett can't play, the Browns have Nate Orchard and Carl Nassib ready opposite Emmanuel Ogbah. Orchard, the Browns' second-round pick in 2015, sat out the final 13 games of last season with an ankle injury, but showed promise at the end of his rookie year.

Nassib, a third-round pick last season out of Penn State, was limited to 2.5 sacks. But regardless of who replaces him, they'll be a dropoff from Garrett, whom the Browns believe can transform their defense.

Steelers coach Mike Tomlin, when asked about Garrett and quarterback DeShone Kizer, noted how good the rookies are.

"Those guys don't need an endorsement from me,'' he said. "They're worthy of their draft positions, and they've proven that. I have a lot of respect for those guys and preparing to compete against them this weekend. They are talented, talented guys.''